Separation string for the separation of hydrocarbon from contaminants in a wellbore and method of assembling same

ABSTRACT

A separation string includes an outer pre-drilled liner and an inner assembly disposed within the outer pre-drilled liner. The inner assembly includes a shear-out member and a filter assembly for separating hydrocarbons from contaminants. A swivel slack joint is connected to an upper end of the inner assembly to facilitate mounting of a top sub to the inner assembly and to the outer pre-drilled liner without producing rotation of the inner assembly. The swivel slack joint includes an outer sleeve connected to the inner assembly, and a tube connected to the top sub. The tube is freely rotatable and vertically slidable relative to the sleeve. The shear-out member is designed to shear at a load less than a load which would cause other components of the inner assembly to shear, and to present, upon shearing, a portion configured to be grasped by a retrieval tool.

FIELD OF THE INVENTION

[0001] The invention relates to a separation string for the separation of contaminants from hydrocarbons in a wellbore and to a method of assembling such a separation string.

BACKGROUND OF THE INVENTION AND BRIEF DESCRIPTION OF THE RELATED ART

[0002] Hydrocarbon gases and liquids have been recovered from underground wellbores for over a hundred years. The recovery technology generally involves drilling a wellbore into a hydrocarbon gas or liquid formation and withdrawing the materials under reservoir pressure or by artificial lifting.

[0003] The current recovery technology involves removing, from the wellbore, the hydrocarbon together with any contaminants which are present, and then separating the contaminants from the hydrocarbon above ground. This above ground separation is costly. Disposal of the removed contaminants may also present environmental problems. The contaminants which may be produced include gases, such as carbon dioxide, nitrogen, water vapor, hydrogen sulfide, helium, and other trace gases, and liquids such as water, and others.

[0004] The contaminants which are brought to the surface and separated from the hydrocarbon must be released to the atmosphere or otherwise disposed of, adding expense to the process. Due to environmental concerns about the release of greenhouse gases, many countries are placing greater limitations on emission of byproduct gases to the atmosphere. For example, some countries now assess a tax on carbon dioxide emissions. Other contaminants are highly corrosive or poisonous and require special handling. For example, hydrogen sulfide must be reacted and converted to molten sulfur before disposal.

[0005] Accordingly, it would be highly desirable to maintain some or all of the contaminant materials within the wellbore and/or selectively separate the contaminants in the wellbore for reinjection, removal, or other processing.

[0006] Membrane technology has been developed which allows the selective passage of materials. This technology has heretofore been used as an above ground, technology for separating hydrocarbons from contaminants after recovery. Although its use in a downhole situation has been proposed, that technology has not actually been used downhole, despite the obvious economic and environmental benefits that could be achieved therefrom. Furthermore, in offshore applications, downhole separation would reduce the amount of heavy and space-consuming equipment present on the offshore deck.

[0007] It has previously been proposed to suspend membrane-carrying tubing in a wellbore for separating hydrocarbon from contaminants (e.g., see U.S. Pat. No. 6,015,011). However, such tubing is lengthy and quite flexible, making it both difficult to control and susceptible to damage while being inserted into a wellbore. In that regard, the membrane filters can be quite brittle and susceptible to breakage in response to the string impacting against the side of the wellbore. Also, due to the manner in which membranes function, even the smallest break or tear can have a significant adverse effect on the performance of the membrane. Moreover, it would be difficult and costly to make such a string having interconnecting thread joints that are rugged enough to withstand the weight and torquing of the string.

[0008] Thus, it would be desirable to provide an apparatus and method for downhole separation and selective recovery to maximize the production of a desired hydrocarbon while minimizing the production of contaminants, utilizing membrane technology.

[0009] It would also be desirable to provide a separation structure which is economical to produce and assemble, as well as being easier to control and less susceptible to damage.

SUMMARY OF THE INVENTION

[0010] One aspect of the present invention involves a separation string for separating hydrocarbons from contaminants in a wellbore. The separation string includes an outer housing, i.e., pre-drilled liner including bottom and top ends spaced apart along a vertical axis of the pre-drilled liner, and an inner assembly disposed inside of the pre-drilled liner. The inner assembly comprises a filter assembly which includes at least one membrane unit adapted to separate at least one hydrocarbon from at least one contaminant. A top sub is threadedly attached to a top end of the outer pre-drilled liner. A swivel slack joint interconnects the top sub and the inner assembly. The swivel slack joint includes first and second telescopingly arranged elements. A bottom end of the first element is attached to a top end of the inner assembly, and a rear end of the second element is threadedly attached to the top sub. The second element is mounted to the first element for vertical sliding movement relative thereto, and being rotatable relative to the first element about a longitudinal axis of the outer pre-drilled liner, to permit the top sub to be screwed to the outer pre-drilled liner without rotating the inner assembly.

[0011] The invention also relates to the method of coupling the pre-drilled liner and the inner assembly to the top sub. The method includes attaching the bottom end of the first element to the top end of the inner assembly. Then, the top sub is screwed to the top end of the second element. Thereafter, the top sub is screwed to the rear end of the outer pre-drilled liner while causing the top sub to rotate the second element relative to both the first element and the inner assembly about the longitudinal axis, to prevent rotation of the inner assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The objects and advantages of the invention will become apparent from the following detailed description of a preferred embodiment thereof in connection with the accompanying drawings in which like numerals designate like elements and in which:

[0013]FIG. 1 is a vertical sectional view taken through an inner assembly of a separation string according to the present invention;

[0014]FIG. 2 is a view similar to FIG. 1 showing the inner assembly being lowered into an outer pre-drilled liner of the separation string;

[0015]FIG. 3 is a view similar to FIG. 2 after a latch-in seal mechanism of the inner assembly has been latched to the bottom of the outer pre-drilled liner;

[0016]FIG. 4 is a view similar to FIG. 3 after the inner assembly has been raised to confirm that latching has occurred;

[0017]FIG. 4A is a fragmentary view of FIG. 4 showing a tubing string being fitted with a top sub;

[0018]FIG. 4B is a view similar to FIG. 4A showing the top sub being screwed onto a pup joint;

[0019]FIG. 4C is a view similar to FIG. 4B showing the top sub being screwed onto the outer pre-drilled liner FIG. 5 is a view similar to FIG. 4 after the top sub has been attached to the outer pre-drilled liner;

[0020]FIG. 6A is a vertical sectional view taken through a swivel slack joint according to the present invention, with a tube element of the joint in an extended state;

[0021]FIG. 6B is a view similar to FIG. 3 with the tube element in a retracted state;

[0022]FIG. 7A is a vertical sectional view taken through a shear-out member prior to shearing;

[0023]FIG. 7B is a view similar to FIG. 7A with the shear-out member in a sheared state;

[0024]FIG. 8 is a vertical sectional view taken through a membrane unit;

[0025]FIG. 9 is a vertical sectional view taken through a prior art latch-in seal mechanism; and

[0026]FIG. 10 is a fragmentary view of FIG. 9.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0027] A fully assembled separation string 10 depicted in FIG. 5 includes an outer pre-drilled liner or outer assembly 12, and an inner assembly 11 disposed inside of the pre-drilled liner. The outer pre-drilled liner 12 has lower and upper ends spaced apart along a vertical axis of the pre-drilled liner. The separation system is comprised of a cylindrical pre-drilled liner 14, a cylindrical latch-in seal housing 16 screwed onto the bottom of the liner 14, and a cylindrical bottom sub 18 screwed onto the bottom of the latch-in seal housing 1 6.

[0028] The inner assembly 11, also shown in FIG. 1, includes a conventional anchor latch-in seal mechanism 28 for latching into the latch-in seal housing 16 (see also FIGS. 9-10), and a shear-out safety joint 30 screwed into the top end of the latch-in seal mechanism 28. That shear-out safety joint includes first and second sections 30A, 30B (see FIGS. 7A, 7B). Section 30A telescopes within section 30B and is held therein by shear pins 30C. O-ring seals 30D are mounted on the outer periphery of the first section 30A. The first and second sections 30A, 30B include internal and external screw threads 30E, 30F, respectively. The screw thread 30F screws onto the latch-in seal mechanism 28. The shear pins 30C are designed to shear at a predetermined load which is lower than that at which other elements of separation string (including membranes as will be explained) will break. Upon shearing of the shear pins, as shown in FIG. 7B, a portion 30G of the second section 30B becomes exposed, which is configured to be readily grasped by a conventional retrieval tool.

[0029] Thus, in the event that the separation string, while being raised, encounters a resistance to travel, e.g., as caused by a sharp curvature in the wellbore, for example, it is assured that the separation string will shear at a location making it readily possible to retrieve the part of the separation string remaining in the wellbore.

[0030] A filter assembly is screwed into the top end of the shear-out safety joint 30 (see also FIG. 8). That filter assembly could comprise various types of filter devices, but preferably comprises one or more hollow tube membrane units 32 of the type described in U.S. Ser. No. 09/640,623, filed Aug. 17, 2000, the disclosure of which is incorporated by reference herein. Each membrane unit 32 (see FIG. 8) includes a pre-drilled tube 32B and bottom and top end caps 32C, 32D, each end cap having screw threads at both ends. Thus, the bottom end cap 32C has an external screw thread 32E at a bottom end thereof, and an internal screw thread 32F at a top end thereof. The screw thread 32E is to be screwed to another internal element of the separation string, e.g. to another membrane unit, or to the top section 30A of a shear-out safety joint for example. The screw thread 32F attaches to an external screw thread of the pre-drilled tube 32B. The top end cap 32D includes an internal screw thread 32G and an internal screw thread 32H. The screw thread 32G screws into an adjacent internal element of the separation string, such as another membrane unit. The screw thread 32H is secured to the pre-drilled tube 32B. At least one cylindrical membrane 321 is disposed within the pre-drilled tube 32B, and an inner perforated tube 32J is positioned inside of the membrane 32I. Thus, the membrane 32I is protected and reinforced on its inner and outer sides.

[0031] The membranes 32I function to separate one or more hydrocarbons from one or more contaminant. Some contaminants which may be removed are gases including carbon dioxide, nitrogen, water vapor, hydrogen sulfide, helium, and other trace gases, and liquids including water, heavy hydrocarbons, and other liquids. The hydrocarbon from which the contaminants are separated may be oil, methane, ethane, propane, or others.

[0032] Screwed into the top of the filter assembly 32 is a swivel slack joint 36 which facilitates assembly of the unit 10, as will be explained. The swivel slack joint 36, best shown in FIGS. 6A and 6B, includes two telescopingly arranged elements, i.e., an outer sleeve 50, and an inner or upper tube 52 which is slidable up and down within the sleeve 50. The sleeve includes an internal screw thread 54 at its lower end and an internal screw thread 56 at its upper end. Threadedly secured to the upper thread 56 is an insert 58 which forms a downwardly facing radial stop shoulder 60 at its lower end. Set screws 62 are screwed radially through an upper end of the sleeve and against the insert 58 to prevent unscrewing of the insert 58.

[0033] The lower end of the inner tube 52 includes a radially enlarged portion 64 which carries seals in the form of O-rings 66 that engage an inner surface of the sleeve 50. The inner tube 52 is freely rotatable relative to the sleeve 50 about a longitudinal axis A of the pre-drilled liner, and is slidable vertically within the sleeve 50 between the shoulder 60 and an upwardly facing ledge 68 formed by the sleeve 50. An upper end of the tube 52 includes an external screw thread 69 adapted to be attached to a top sub 70.

[0034] The conventional latch-in seal mechanism 28, depicted in FIGS. 9 and 10, includes first and second segments 80, 82 screwed together. The top segment 80 is threadedly secured to the shear-out safety joint 30. The second segment 82 carries external teeth 86 that are engageable with corresponding teeth 88 formed on an inner bore of the latch-in seal housing 16 in response to downward movement of the first segment 80 within the latch-in seal housing 16.

[0035] In practice, the separation string 10 can be assembled while suspended in a wellbore B. The pre-drilled assembly 14, 16, 18, having already been formed, is suspended in the wellbore B by a gripping mechanism G, as shown in FIG. 2. The anchor latch-in seal mechanism 28 is inserted, and then the shear-out safety joint 30 is screwed into the anchor latch-in seal mechanism 28. The tubular membrane units 32 of the filter assembly are screwed together, with the lowest membrane unit being screwed into the top of the shear-out safety joint 30. In practice, there will likely be many membrane units provided, and a number of shear-out safety joints 30.

[0036] A top sub is to be attached to upper ends of both the outer assembly and the inner assembly. Ideally, that should be done without rotating the inner assembly relative to the outer assembly, because such rotation could overtorque and damage the internal components, and/or tear the various seals. The function of the swivel slack joint 36 is to enable such rotation of the inner assembly to be avoided.

[0037] The lower end of the sleeve 50 of the swivel slack joint is next screwed onto the top of a pup joint 71, the lower end of which is secured to the filter assembly. Then, with the tube 52 in its upwardly slid state shown in FIGS. 1, 2 and 6A, a pup joint 73 is screwed into engagement with the upper end of the tube 52 (see FIG. 2). The pup-joint 73 and the inner assembly are lowered into the pre-drilled liner on a tubing string 72 until the anchor latch-in mechanism 28 lands on a locating shoulder 88 formed in the latch-in seal housing 16. A small amount of tension is then applied by the tubing string 72 to the inner assembly by lifting the tubing string (see FIG. 4), to give a positive indication that the anchor latch-in mechanism 28 is properly latched into the latch-in seal housing 16. At this point, the upper tube 52 of the swivel slack joint is fully extended (as shown in FIGS. 4 and 6A), and the upper facing ledge 68 of the upper tube 52 is supporting the downward facing shoulder 60 of insert 58. The tubing string 72 is then separated from the pup joint 73 and the top sub 70 is attached to the tubing string (see FIG. 4A). The tubing string 72 is then lowered to position the top sub on the upper end of the upper tube 52. By then rotating the tubing string 72, and thus the top sub 70, the top sub becomes screwed onto the pup joint 73 (see FIG. 4B). Then, the tubing string 72 is lowered, and the fully extended upper tube 52 of the swivel slack joint starts to slide toward the bottom of the sleeve 50 of the swivel slack joint. At some point before the bottom of the tube 52 reaches the ledge 68 of the sleeve 50, the outer threads 70A of the bottom of the top sub 70 will engage the inner threaded portion of the pre-drilled liner 14. Further rotation of the tubing string 72 and the top sub 70 causes the top sub to be screwed onto the pre-drilled 14. As this occurs, the tube 52 is rotated by the top sub. However, since the tube 52 can rotate relative to the sleeve 50 about a longitudinal axis of the casing, the inner assembly 28, 30, 32 is not rotated, so no damage occurs to the inner assembly. Relative longitudinal movement between the inner and outer assemblies is accommodated by the ability of the tube 52 to retract downwardly within the sleeve 50.

[0038] After the top sub 70 has been fully screwed down, the separation string 10 appears as shown in FIG. 1 and can be lowered within the wellbore, to enable the bottom sub 18 to be connected to any suitable downhole element, such as a packer for example.

[0039] If desired, one or more conventional pack-off (seal) assemblies could be provided as part of the separation string, to bear against an inner surface of the casing, in order to stabilize the separation string within the pre-drilled.

[0040] The filter membrane 321 is protected on its inner and outer sides by pre-drilled structures 32B and 32J and thus is less likely to fracture or otherwise be damaged while being run into and out of the wellbore.

[0041] The membrane units of the filter assembly have a tubular configuration and form part of an open central passageway of the separation string. This tubular configuration allows conventional oil field tools to be run through the separation string. The ability to run tools through the separation string provides the advantage that the separation string does not have to be removed for many well work processes to be performed. For example, gas lift valves, setting and pulling tools, impression blocks, chemical injection valves, tubing stops, packers, tubing plugs, memory logs, production logs, dump bailers, perforation guns, or the like can be run through the separation string.

[0042] The operation of the present invention has been described with respect to a vertical well, however, it should be understood that the invention may be employed in horizontal wells and other non-vertical wells.

[0043] During a production operation, the hydrocarbon and contaminants enter the wellbore and pass upward through the central passageway of the separation string. As the hydrocarbon passes through the filter assembly 32, one or more contaminants permeate out through the membrane units and enter a surrounding containment collection zone. The hydrocarbon, plus any remaining contaminants that were not removed, continue out the top of the separation string. The hydrocarbon with reduced contaminants is passed to the surface or to another separation system. The contaminants which have been collected in the collection zone may be disposed of by directing the contaminants to an underground disposal formation. Alternatively, the contaminants may be removed from the collection zone to the surface.

[0044] It will be apparent that the swivel slack joint 36 of the present invention permits a top sub to be screwed onto an inner assembly which include membrane filters without producing rotation of the inner assembly, and thereby minimizes chances that the inner assembly will be damaged during attachment of the top sub.

[0045] Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims. 

What is claimed is:
 1. A separation string for separating hydrocarbons from contaminants in a wellbore, comprising: an outer pre-drilled liner including bottom and top ends spaced apart along a vertical axis of the casing; an inner assembly disposed inside of the pre-drilled liner and comprising a filter assembly including at least one membrane unit adapted to separate at least one hydrocarbon from at least one contaminant; a top sub threadedly attached to the top end of the outer pre-drilled liner; and a swivel slack joint interconnecting the top sub and the inner assembly, the swivel slack joint including first and second telescopingly arranged elements, a bottom and of the first element attached to a top end of the inner assembly, and a top end of the second element threadedly attached to the top sub, the second element being mounted to the first element for vertical sliding movement relative thereto, and being rotatable relative to the first element about the longitudinal axis, to permit the top sub to be screwed to the outer pre-drilled liner without rotating the inner assembly.
 2. The separation string according to claim 1 wherein the first element of the swivel slack joint comprises a sleeve having a screw thread at its bottom end; the second element comprising a tube slidably mounted inside the sleeve and having a screw thread at its top rear end.
 3. The separation string according to claim 2 wherein the swivel slack joint further includes an insert attached to a top end of the sleeve and defining a shoulder for limiting rearward movement of the tube relative to the sleeve.
 4. The separation string according to claim 3 wherein the insert is threadedly secured to the top end of the sleeve and further attached thereto by set screws for preventing unscrewing of the insert.
 5. The separation string according to claim 3 wherein one of the sleeve and the tube carries seals bearing against the other of the sleeve and the tube.
 6. The separation string according to claim 5 wherein the seals comprise O-rings mounted on an outer periphery of a front portion of the tube.
 7. The separation string according to claim 1 wherein the inner assembly further includes a shear-out member having a shearing portion which shears at a predetermined load less than a load at which other components of the inner assembly would shear, the shear-out member including a portion which is exposed in response to a shearing of the shearing portion and which is configured to be grasped by a retrieval tool.
 8. The separation string according to claim 1 wherein the membrane unit comprises an outer pre-drilled tube, and a pair of end caps screwed to opposite ends of the tube to retain a membrane inside of the tube.
 9. The separation string according to claim 8 wherein the membrane unit further comprises an inner pre-drilled tube disposed inside of the membrane.
 10. The separation string according to claim 1 wherein the inner assembly further includes a latch assembly for latching the inner assembly to the outer pre-drilled liner.
 11. A separation string for separating hydrocarbons from contaminants in a wellbore, comprising: an outer pre-drilled liner including bottom and top ends spaced apart along a vertical axis of the pre-drilled liner; an inner assembly disposed inside of the casing and comprising: a latch member for latching the inner assembly to the outer pre-drilled liner casing; a filter assembly comprising at least one membrane adapted to separate at least one hydrocarbon from at least one contaminant, and a shear-out member for shearing at a predetermined load less than a load which would fracture the other components of the inner assembly and including a portion which becomes exposed in response to a shearing of the shear-out member and configured for being grasped by a retrieval tool; and a swivel slack joint interconnecting the top sub and the inner assembly, the swivel slack joint including first and second telescopingly arranged elements, a bottom end of the first element attached to a top end of the inner assembly, and a top end of the second element threadedly attached to the top sub, the second element being mounted to the first element for vertical sliding movement relative thereto, and being rotatable relative to the first element about the longitudinal axis, to permit the top sub to be screwed to the outer casing without rotating the inner assembly.
 12. A method of assembling a separation string, the separation string including an outer pre-drilled liner and an inner assembly disposed within the outer pre-drilled liner, the pre-drilled liner including bottom and top ends spaced apart along a longitudinal axis of the pre-drilled liner, the inner assembly comprising a filter assembly including at least one membrane unit for separating at least one hydrocarbon from at least one contaminant, the method comprising the steps of: A. providing a swivel slack joint in the casing at a top end of the inner assembly, the swivel slack joint including first and second telescopingly arranged elements, the second element being slidable relative to the first element along the vertical axis, and rotatable relative to the first element about that axis; B. attaching a bottom end of the first element to a top end of the inner assembly; C. screwing a top sub to a top end of the second element; and D. screwing the top sub to a top end of the outer pre-drilled liner while causing the first sub to rotate the second element relative to both the first element and the inner assembly about the longitudinal axis, to prevent rotation of the inner assembly. 